The present invention relates to a method of producing a printed packaging laminate in web form, comprising the steps of coating a material web in full width with one or more layers of thermoplastic material, and splitting the web by means of longitudinal incisions. The present invention also relates to an apparatus for carrying the method into effect.
In the conventional production of packaging material webs of the type which is employed for manufacturing single-use disposable packages for, for example, milk or juice, a laminated material is progressively created which comprises one or more carrier layers of relatively rigid material, e.g. fibre or foamed plastic material. On either side of the carrier layer, one or more layers of thermoplastic material, e.g. polyethylene, are progressively laminated in order, on the one hand, to impart strength to the laminate and, on the other hand, to ensure that the material obtains the requisite liquid- and gas-tightness. In those case when additional gas- and possibly light-tightness are desired, the laminate is provided with additional layers of barrier material, e.g. aluminium foil or different types of barrier plastics. The laminate is also provided with external decorative artwork by a printing process, and is normally moreover subjected to a mechanical processing with a view to producing a previously determined pattern of weakening lines, so-called crease lines, in order to facilitate folding and subsequent reforming of the laminate into individual packaging containers.
Traditionally, machine production of printed and creased packaging laminate encompasses a number of production stages between each one of which the packaging material web is rolled up in reel form and moved between different production equipment, e.g. for plastic coating, printing of material or splitting or dividing the material into several webs of the desired final width.
In a first production stage, the printing of the material web normally takes place, which is undertaken on a material web having slightly greater width than the total width of the final material webs. This is linked to the fact that printing of the material web cannot take place outside the longitudinal edges of the material web, and in order to make for a certain tolerance, the material web hence is of a width which exceeds by 5 to 50 cm the overall total width of the webs of final width into which the full-width web is subsequently to be split. After the printing, the material web is rolled up and transferred to a coating unit where the material web is unwound and caused to pass a number of extruders which provide the material web with the desired number of layers of thermoplastic material. In this unit, the web is possibly also provided with additional layers of, for example, aluminium foil or some other barrier material. The coating and possible application of, e.g. aluminium foil also takes place with a certain excess width, which implies that the material web, before once again being wound up, is subjected to an edge cutting which removes surplus plastic and possibly a surplus of, for example, the aluminium foil.
The material web which is thus wound up after the coating is once again unwound in a subsequent cutting unit in which the material web, by longitudinal incisions, is split into the desired number of webs of final width. Simultaneously with this splitting operation, an adjustment of the total width of the web also takes place in that the edge regions at both sides of the web are cut away. In such instance, int. al. the unprinted edge of the web is removed, as previously mentioned. After renewed winding up of the individual webs of final width, these are ready to be placed in a packing and filling machine or alternatively rewound and divided into individual sheets or packaging container blanks.
As will have been apparent from the foregoing, the production of laminated packaging material with current methods is quite complicated and includes, among other things, a number of winding up operations of the material web, several edge cutting operations including waste management, and several rewinding operations. Moreover, present methods result in a relatively large quantity of waste occurring, principally in the edge cutting operation, but also in the rewinding operations, since the outermost end sections of the material cannot be used. A major drawback is moreover that the printing of the material, as was mentioned above, must take place with printing rollers which are of greater width than is actually necessary. This entails that the stereos must have a larger surface area, which increases the stereo price since this is directly related to the surface area of the stereos. If one considers that, in the normal printing of high quality packaging material for, for example juice packages, printing is often done with eight colours, it will be readily understood that the cost for stereos is greatly increased because of the above-mentioned safety margins.
There is thus a general need in the packaging materials industry to realise a method for the production of printed, plastic-coated packaging laminate which takes it possible to greatly reduce the amount of waste in the production process and also reduce the area of the xe2x80x9cunnecessaryxe2x80x9d stereo surface.
One object of the present invention is thus to realise a method of producing printed packaging laminate in web form, the method making it possible to reduce the need of edge cutting of the packaging material web and thereby reduce the quantity of waste material, as well as the costs for the waste material, and its management.
A further object of the present invention is to realise a method of producing printed packaging laminate in web form, the method making it possible to print the material with a stereo width which corresponds to the desired, final printing width.
Yet a further object of the present invention is to realise a method of producing printed packaging laminate in web form, the method simplifying the production process and reducing the number of rewindings of the material.
Still a further object of the present invention is finally to realise a method of producing printed packaging laminate in web form, the method considerably reducing the costs and simplifying the production of finished packaging laminate.
The above and other objects have been attained according to the present invention in that a method of the type described by way of introduction has been given the characterising feature that the material web is split into semi-webs each one of which being provided with a printed area centred in relation to a longitudinal centre line, and is split into two webs of a final width by incisions along this centre line.
Preferred embodiments of the method according to the present invention have further been given the characterising features described herein.
The present invention also encompasses an apparatus for carrying the method according to the present invention into effect.